You are probably looking at a rather mathematical sketch of an algorithm. There are two general roads to implement non-trivial mathematical expressions such as series, integrals, and differential equations.

 1. If you want exact, potentially symbolic results you have to simplify "complex" expressions into closed forms on paper, and/or employ _computer algebra_.
 2. If you are satisfied with numerical, potentially approximate solutions, you want to employ _numerical algorithms_, including error estimations.